Certain embodiments of the invention relate to apparatus and methods for, converting optical pulses from compact fiber laser pulse sources into pulses having different wavelengths and having a large or increased bandwidth through the use of optical parametric amplifying media. Other embodiments of the invention relate to apparatus and methods for producing short optical pulses utilizing amplification in optical fibers operating in the infrared region beyond about 1700 nm.
Nonlinear optical elements may be employed to provide amplification in a process know as optical parametric amplification (OPA). In such a process, an intense coherent pump beam at a first wavelength interacts with the nonlinear optical element such as a nonlinear optical crystal to produce amplification. One or two output beams at respective second and third optical wavelengths exit the nonlinear optical element. These output beams are referred to as the signal and the idler. In optical parametric amplification, in addition to being pumped, the nonlinear optical element is seeded with radiation at the signal and possibly idler wavelengths.
The optical parametric amplification process obeys the conservation of energy principle ω1=ω2+ω3, where ω1 is the pump frequency and ω2 and ω3 are the signal and idler frequencies. The individual values of ω2 and ω3 also satisfy the conservation of momentum condition, which for plane wave intersection is k1=k2+k3 where k1, k2, and k3 are the respective wavenumbers for ω1, ω2, and ω3. This later condition provides for phase-matching. Phase matching can be varied by changing an appropriate phase matching parameter of the nonlinear optical element such as the angle of propagation or the temperature.
If is no light is supplied to the nonlinear optical element at ω2 or ω3, the process is referred to as optical parametric generation (OPG). In OPG, seeding is provided by noise.
When ω2=ω3, the process is termed degenerate.
Parametric amplification can be incorporated in a resonant cavity that circulates the signal and/or the idler. In this geometry, the process is termed parametric oscillation. A parametric amplifier inside a resonant optical cavity yields a laser that can be used to generate a frequency-tunable coherent beam of light by pumping with a beam of fixed frequency. This laser is tuned by varying the phase matching properties of the nonlinear optical element.
Unique apparatus and methods of implementing optical parametric amplification and optical parametric generation are presented below.